Cardiac stimulation devices, including implantable cardiac pacemakers and implantable cardioverter defibrillators (ICDs), are electrically connected to the heart by at least one cardiac lead. Cardiac leads may be introduced transvenously and advanced through a venous pathway to a cardiac implantation site. For example, endocardial leads are commonly used to provide an electrical pathway between a pacemaker or ICD, connected to the proximal end of the lead, and one or more electrodes at the distal end of the lead that are in contact with endocardial tissue, typically within a right heart chamber. In such a manner, electrical pulses emitted by the pacemaker or ICD travel through the endocardial lead and stimulate the heart. Cardiac signals arising from the heart may be received by the lead electrodes and carried back to the device by the endocardial lead.
Transvenous leads may also be used for providing an electrical pathway to the left chambers of the heart. A transvenous lead may be advanced into the coronary sinus and further into the cardiac veins for stimulating the left atrial or left ventricular epicardial tissue and for sensing cardiac signals. It is desirable to advance coronary sinus leads deep into the cardiac veins in order to effectively stimulate and sense in the left ventricle.
When transvenous leads are implanted with the use of a guide catheter, some difficulties arise pertaining to the leads' electrical connectors. One difficulty arises when electrical testing must be performed at the time of implant. When transvenous leads are implanted it is common practice to test the position of the leads' electrodes for efficacy and efficiency of pacing, sensing and/or defibrillation. If the length of a lead is not sufficiently longer than that of a guiding catheter used to implant the lead, the lead's connector may be covered up by the guide catheter that is pulled back, proximally, to exposed the lead's electrodes; thus, connections cannot be made at the connector for electrical testing. Another difficulty arises if the lead connector assembly is sized to fit a standard device connector port. Such connectors generally have a larger diameter than the lead body so that a guiding catheter having a lumen sized for the lead body cannot be removed over these connectors. Pacemakers and ICDs are typically provided with connector ports conforming to an industry standard size. For example, an IS-1 connector port provides a 3.2 mm in-line electrical connector bore for receiving an IS-1 electrical lead connector of the type generally used to couple to cardiac pacing and sensing electrodes.